1. EMIS 8374 Search Algorithms: DFS Updated 12 February 2004

2. Depth-First Search
Always pick the last (most recently added) node in the LIST
Pick marked nodes in a last-in, first-out order (LIFO)
Breadth-First Search uses a FIFO order
Makes a “deep” probe, creating as long a path as possible
Backs up when it can’t mark a new node

3. Depth-First Search 1 2 4 3 5 6

4. Depth-First Search 5 2 1 2 4 3 5 6 4 6 3 List = {} List = {1}

5. Depth-First Search Tree5 2 2 4 1 6 1 4 3 5 6 3

6. Properties of a DFS Tree
If node j is a descendant of node i, then order(j) > order(i)
All descendants of any node are ordered consecutively in sequence.
That is, suppose that order[i]= p and i has q descendants. Then, any node j such p+1 ≤ order[j] ≤ p+q is a descendant of node i.

7. A Depth-First Search Tree5 1 2 4 3 5 6 3
Order visited =

8. Not A Depth-First Search Tree4 2 2 4 1 6 1 6 3 5 3 5
Order visited =